mstsc.exe multimon broken on Windows 11 25H2 (26200) - second monitor not transmitted to RDP server

After upgrading to Windows 11 25H2 (Build 26200.8655), RDP multimon

connection to a remote machine (also Windows 11 25H2, Build 26200.8457)

fails with error 0x3 / 0x11.

Environment:

• Client: Windows 11 Pro for Workstations, Build 26200.8655
• Server (VDI): Windows 11 25H2, Build 26200.8457
• mstsc.exe version on client: 10.0.26100.8521
• Two monitors: 1920x1080 each, same scale (100%), contiguous

Root cause identified:

• mstsc.exe version remains 26100.x after OS upgrade to 26200 (25H2)
• RdpIdd.dll on server also remains version 26100.x after OS upgrade
• Server-side logs (RdpCoreTS/Operational) show only one monitor received from client: "monitor 0: (1918, 910), source: (0, 0)" Second monitor is never transmitted by client
• System log shows UMDFVerifierFailure for RdpIdd.dll when multimon is attempted

Steps to reproduce:

1. Connect from Windows 11 25H2 client with mstsc /multimon or use multimon:i:1 in RDP file
2. Connection fails with error code 0x3 / extended error 0x11
3. Connection succeeds with use multimon:i:0 (single monitor)

Expected: multimon RDP connection works as it did before 25H2 upgrade

Actual: error 0x3/0x11, server receives only one monitor from client

mstsc.exe and RdpIdd.dll were NOT updated to 26200.x version

during OS upgrade from 24H2 to 25H2. This appears to be the

root cause. SFC /scannow and DISM /RestoreHealth do not fix it.

Repair upgrade via ISO also does not update these components.

Please update mstsc.exe and RdpIdd.dll to 26200.x in the next

cumulative update.